Answers to Part 3 Exercises

	Answers to Part 3 Exercises

	Solution to Copy and Decapitalize Problem

	One straightforward solution is:

	global /^CHAPTER/ mark a \| copy $ \| 'a substitute /APTER/apter/

	which marks the original line, then copies it in its all-caps version
	to the end of the file, and finally returns to the original line to run
	the decapitalizing substitution.

	Another, not quite so obvious but just as good, is to decapitalize
	"CHAPTER" first, then copy the decapitalized version to the end of
	the file, and finally run a substitution command on the current line
	(which is now the copied line at the end of the file) which changes the
	capitalization back to "CHAPTER".


	Solution to troff Problem

	The command line:

	1 , 16 global /^/ 217 substitute /n(PDu/\\n(PDu/

	does it by running the substitution command 16 times. Each time it
	inserts a single backslash. (The double backslash in the replacement
	pattern is necessary because the backslash is a special character
	even there.)


	Hint for Numbering Problem

	My solution to this problem has an intermediate stage in which each
	macro is followed by a string of capital I letters on the same line.
	The count of the capital I letters on any macro line is equal to the
	paragraph number. That is, the macro line for the fifth paragraph looks
	like this in the intermediate stage:

	.ppIIIII


	Solution to Numbering Problem

	The paragraphs can be numbered with just two global
	commands. The first one:

	global /^\.pp/ . , $ substitute //.ppI/

	goes to each line beginning with a start-of-paragraph macro, then
	runs a substitute command from that line through the end
	of the file that puts a capital letter I after each such macro. So the
	substitute command that runs from the first marked line
	puts an I after every one of the macros; from the second marked line it
	puts an I after every such macro except the first; from the third marked
	line it puts an I after every such macro except the first and the second;
	and so on. Thus, after this global finishes, you have a
	string of the letter I after every macro that is equal in number to the
	paragraph's number. That is, after the macro for the third paragraph you
	have the string "III"; after paragraph 5 you have the string "IIIII";
	etcetera. Already you have Roman numerals (of a very primitive sort)
	numbering the paragraphs.

	A second global command puts those Roman numerals into canonical
	form:

	global /^\.pp/ substitute /IIIII/V/ g \
	\| substitute /VV/X/ g \| substitute /IIII/IV/

	(As you'll learn in the next installment of this tutorial, a lower-case
	letter g at the end of a substitute command tells the
	editor to perform the substitution as many times as it can on each line,
	and a backslash at the end of a partial command line means the next line
	continues the command string.)

	To see how our second global command sets things right,
	consider the case of the 19th paragraph. The next four lines show what
	the macro line looks like at the start of the command and how it has
	changed after each of the three substitute commands has
	done its work:

	.ppIIIIIIIIIIIIIIIIIII
	.ppVVVIIII
	.ppXVIIII
	.ppXVIV

	(Astute readers will realize that the paragraphs could have been
	numbered with just one global command. Each macro line
	has all the capital I letters it will get before global
	leaves it for the next line. So we could have had the command string
	start by marking the line, next run the substitution that adds a capital
	I to all remaining macro lines, then return to the line and run the
	substitutions that produce a true Roman numeral.)

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